By searching for "How to submit a sitemap to Google" you can find dozens of links, and all of'em truly explain the how to very well.

But all of'em start with this first step:

Login to your Google Webmaster Tools

...

My problem is that, we are creating a hosted-CMS solution (something similar to wordpress.com), and we let people assign their domains to their sites. However, we don't want to ask them to create Google Webmaster Tools account, and follow a mid-technical path, to get their sites indexed.

Rather, we want to anonymously submit their Sitemaps (like http://domain/sitemap, where domain is a variable) to Google.

We found this link, at the end of which, it's explained that you can submit your sitemap to this URL:

www.google.com/webmasters/tools/ping?sitemap=sitemap_url

However, I'm not sure if it's really anonymous or not. Is it a good idea at all or not? Do we have other options to notify Google to index our sites?

1 Answer
1

You can specify the location of the Sitemap using a robots.txt file.
To do this, simply add the following line including the full URL to
the sitemap:

Sitemap: http://www.example.com/sitemap.xml

This directive is independent of the user-agent line, so it doesn't
matter where you place it in your file. If you have a Sitemap index
file, you can include the location of just that file. You don't need
to list each individual Sitemap listed in the index file. You can
specify more than one Sitemap file per robots.txt file.

Even better is that many other search engines besides Google understand this directive too, so you get your sitemap submitted to all of them.
–
Ilmari KaronenMar 1 '12 at 15:24

It's probably worth setting the sitemap in the robots.txt and also pinging google to let it know where the sitemap is... might get things moving quicker otherwise you are relying on google discovering your site naturally.
–
Vince PettitMar 1 '12 at 16:41